1,764 research outputs found
Black-hole kicks from numerical-relativity surrogate models
Binary black holes radiate linear momentum in gravitational waves as they
merge. Recoils imparted to the black-hole remnant can reach thousands of km/s,
thus ejecting black holes from their host galaxies. We exploit recent advances
in gravitational waveform modeling to quickly and reliably extract recoils
imparted to generic, precessing, black hole binaries. Our procedure uses a
numerical-relativity surrogate model to obtain the gravitational waveform given
a set of binary parameters, then from this waveform we directly integrate the
gravitational-wave linear momentum flux. This entirely bypasses the need of
fitting formulae which are typically used to model black-hole recoils in
astrophysical contexts. We provide a thorough exploration of the black-hole
kick phenomenology in the parameter space, summarizing and extending previous
numerical results on the topic. Our extraction procedure is made publicly
available as a module for the Python programming language named SURRKICK. Kick
evaluations take ~0.1s on a standard off-the-shelf machine, thus making our
code ideal to be ported to large-scale astrophysical studies.Comment: More: https://davidegerosa.com/surrkick - Source:
https://github.com/dgerosa/surrkick - pypi:
https://pypi.python.org/pypi/surrkick - Published in PR
High-accuracy mass, spin, and recoil predictions of generic black-hole merger remnants
We present accurate fits for the remnant properties of generically precessing
binary black holes, trained on large banks of numerical-relativity simulations.
We use Gaussian process regression to interpolate the remnant mass, spin, and
recoil velocity in the 7-dimensional parameter space of precessing black-hole
binaries with mass ratios , and spin magnitudes .
For precessing systems, our errors in estimating the remnant mass, spin
magnitude, and kick magnitude are lower than those of existing fitting formulae
by at least an order of magnitude (improvement is also reported in the
extrapolated region at high mass ratios and spins). In addition, we also model
the remnant spin and kick directions. Being trained directly on precessing
simulations, our fits are free from ambiguities regarding the initial frequency
at which precessing quantities are defined. We also construct a model for
remnant properties of aligned-spin systems with mass ratios , and spin
magnitudes . As a byproduct, we also provide error
estimates for all fitted quantities, which can be consistently incorporated
into current and future gravitational-wave parameter-estimation analyses. Our
model(s) are made publicly available through a fast and easy-to-use Python
module called surfinBH.Comment: 6+5 pages. Matches PRL version. Python implementation available at
https://pypi.org/project/surfinBH
Transport and magnetic properties in YBaCo2O5.45: Focus on the high-temperature transition
The electronic transport properties and the magnetic susceptibility were
measured in detail in . Close to the so-called metal-insulator
transition, strong effects of resistance relaxation, a clear thermal hysteresis
and a sudden increase of the resistance noise are observed. This is likely due
to the first order character of the transition and to the underlying phases
coexistence. Despite these out of equilibrium features, a positive and linear
magneto-resistance is also observed, possibly linked to the heterogeneity of
the state. From a magnetic point of view, the paramagnetic to ordered magnetic
state transition is observed using non linear susceptibilty. This transition
shows the characteristics of a continuous transition, and time dependent
effects can be linked with the dynamics of magnetic domains in presence of
disorder. Thus, when focusing on the order of the transitions, the electronic
one and the magnetic one can not be directly associated.Comment: accepted for publication in PR
FIB-SEM Nanotomography in Materials and Life Science at EPFL
Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 - August 5, 201
3D EDX microanalysis by FIB-SEM: Elemental quantification enhancement
Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 - August 2, 201
Field-Induced Magnetization Steps in Intermetallic Compounds and Manganese Oxides: The Martensitic Scenario
Field-induced magnetization jumps with similar characteristics are observed
at low temperature for the intermetallic germanide Gd5Ge4and the mixed-valent
manganite Pr0.6Ca0.4Mn0.96Ga0.04O3. We report that the field location -and even
the existence- of these jumps depends critically on the magnetic field sweep
rate used to record the data. It is proposed that, for both compounds, the
martensitic character of their antiferromagnetic-to-ferromagnetic transitions
is at the origin of the magnetization steps.Comment: 4 pages,4 figure
Debate: Transfusing to normal haemoglobin levels will not improve outcome
Recent evidence suggests that critically ill patients are able to tolerate lower levels of haemoglobin than was previously believed. It is our goal to show that transfusing to a level of 100 g/l does not improve mortality and other clinically important outcomes in a critical care setting. Although many questions remain, many laboratory and clinical studies, including a recent randomized controlled trial (RCT), have established that transfusing to normal haemoglobin concentrations does not improve organ failure and mortality in the critically ill patient. In addition, a restrictive transfusion strategy will reduce exposure to allogeneic transfusions, result in more efficient use of red blood cells (RBCs), save blood overall, and decrease health care costs
Changes in hemlock looper [Lepidoptera: Geometridae] pupal distribution through a 3-year outbreak cycle
La distribution des chrysalides de l’arpenteuse de la pruche, Lambdina fiscellaria, a été étudiée au cours d’un cycle épidémique d’une durée de trois ans près du Lac Princeton sur l’île d’Anticosti au Québec. Au total, 10 sapins ont été coupés et toutes les chrysalides ont été comptées sur le tronc et les branches (partie non-foliée vs foliée) de la cime inférieure, médiane et supérieure, ainsi que sur le tronc sous la cime. En condition préépidémique, les chrysalides ont principalement été trouvées sur les branches des cimes médianes et supérieures. Durant l’épidémie, la densité des chrysalides n’a pas augmenté dans ces sites de pupaison et les larves se sont surtout transformées en chrysalides sur le tronc, à partir du sol jusque dans la cime médiane, ainsi que sur les branches de la cime inférieure. Peu de chrysalides ont été trouvées sur la partie foliée des branches en période post-épidémique, la plupart étant trouvées sur la partie basale non-foliée qui apparaît comme un endroit préférentiel pour la pupaison de l'arpenteuse de la pruche. De façon à optimiser la détection des augmentations de populations dans les réseaux de surveillance, des pièges à chrysalides devraient être placés à hauteur de poitrine sur le tronc de sapins baumiers.The hemlock looper, Lambdina fiscellaria, pupal distribution was studied through a 3-year outbreak cycle near Lac Princeton on Anticosti Island in Quebec. Over the 3 years, 10 balsam fir trees were cut and all pupae were counted on the stem and branches (non-foliated vs foliated parts) of the lower, middle and upper crowns and on the stem below crown. In pre-outbreak conditions, pupae were mostly found on branches of the middle and upper crowns. During the outbreak, pupal density did not increase on these parts of the trees, since pupae were mostly found on the stem, from the ground to the middle crown, and on branches of the lower crown. Few pupae were found on the foliated portion of branches in post-outbreak conditions but most were found on the basal non-foliated part of branches, which appears to be a preferred location for hemlock looper pupation. In order to optimize detection of population increases in monitoring networks, we suggest using pupal traps at breast height on balsam fir trees
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